This photo provided by the Washington State Patrol shows the aftermath of a mudslide that struck a house with people inside in Snohomish County on Saturday March 22, 2014. / AP

by KING-TV, Seattle

by KING-TV, Seattle

SEATTLE -- Rescue crews are searching for survivors after a huge mudslide came down on homes in Snohomish County in northwest Washington, killing at least three.

County officials said Saturday night that they could hear cries for help from people trapped under debris.

"We're going to take extreme risk to get them out of here tonight," said John Pennington with the Department of Emergency Management.

Snohomish County Fire District 21 Chief Travis Hots said it wasn't clear how many people might still be alive.

Three people were killed and at least six houses were destroyed.

At least eight people, including a six-month-old baby boy, were taken to a local hospital. The infant is in critical condition at Harborview Medical Center in Seattle, according to AP.

The slide cut off the city of Darrington and dammed up the North Fork of the Stillaguamish River, causing the water to pool behind the dam.

First responders in Snohomish County called it the worst slide, the worst natural disaster, they've seen in decades.

"Think back to what Mount St. Helens and Toutle River looked like -- and that's what we're looking at," said Rodney Rochon, of the Snohomish County Sheriff's Office.

The National Weather Service said the river level dropped from 3.1 feet to 0.9 feet in the hour after the slide occurred, confirming the river was blocked by the slide.

The state hydrologist measured 15-20 feet of debris blocking the river but a catastrophic flood event is unlikely, said KING 5 Meteorologist Mary Lee.

Since the landslide the river flow is 1,000 cubic feet per second, the National Weather Service said. For flooding to occur it would need to be 36,000 cubic feet per second.

For a catastrophic flood event to occur there would need to be a complete blockage for 36 hours with water suddenly released within an hour's time.

Snohomish County officials advised residents downstream of the slide to evacuate their homes.

"It is going to break loose and the question is how and where," said John Pennington with the Department of Emergency Mgt.

Hospital spokeswoman Susan Gregg said two adult victims were in critical condition - an 81-year-old man and a 58-year-old man - while a 37-year-old man was in serious condition. Gregg said Harborview had one other male patient from the landslide, but no information on his condition was available.

Five of the injured were brought to Cascade Valley Hospital in Arlington, and one has already been treated and released, said hospital spokeswoman Jennifer Egger. She didn't know the condition of the others.

Shelters have been set up at Post Middle School in Arlington and the Darrington Community Center. The Red Cross is assisting.

Officials warned people to stay clear of all trestles and bridges on the north fork of the river.

The landslide completely covered State Route 530 near the town of Oso, about 55 miles north of Seattle. It was at least 135 feet wide and 180 feet deep and hit just before 11 a.m., Snohomish County authorities said.

Paulo Falcao told KING 5 the slide came down right in front of him.

"I was coming down the hill and I just saw darkness, like somebody wants to grab you, and everything was gone," he said

Another person said he could hear the screams of a baby so he and a Trooper rushed in to help.

More than 100 first responders converged on the scene, including those from Washington State Patrol, Department of Transportation, Department of Emergency Management, US Navy, Snohomish County Sheriff's Office and most all of the fire department agencies in north Snohomish County.

The National Weather Service has issued a flash flood watch for Snohomish County through Sunday afternoon.